The present invention relates to a high pressure gate valve for controlling the flow of a fluid through a pipe. Conventional gate valves comprise a gate element which is movable in a direction perpendicular to the flow of the pipe in order to allow or block the flow of a fluid. In the closed position, high pressure fluid on the inlet side collects and biases the valve towards the closed position. This can cause a condition called pressure lock, wherein the pressure build up prevents the valve from opening.
When the fluid is of a relatively low pressure, such as below 100 bar, this does not pose a problem, as it does not take much force to overcome the pressure lock caused by the fluid when it is desired to open the valve. However, when the fluid is highly pressurised the valve may become stuck in the closed position unless a very large input force is used. Highly pressurised may apply to a pressure of over 100 bar, in the present invention pressures in the order of 1000 bar are considered.
Conventional gate valves deal with this by comprising an additional valve stem with a ball screw in order to balance the pressure thrust. This is a complicated design and requires a number of moving components. Alternatively, equalising pipes and relief valves are fitted. However, these are not ideal as they complicate the process of opening the valve by requiring manual intervention as well as requiring a further piping component which may fail. Thus the installation of the valve is more complex and takes up more space.